264 MISSISSIPPIAN BRACHIOPODA 



DlELASMA INFLATA n. Sp. 



Plate XXXII, Figs. 18-28 



1894. Dielasma turgida Hall and Clarke, Int. to Study of Brach., pi. 53. 



fig. 12, (not figs. 10-11). 



1895. Dielasma turgida Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 81, 



fig. 4 (not figs. 1-3, 5-8). 



Description. Shell below medium size, longer than wide, subovate or 

 subangularly subpentagonal in outline, the greatest width near or ante- 

 rior to the middle, the anterior margin emarginate or slightly convex, the 

 valves gibbous, often geniculate near the middle, the thickness of the 

 shell sometimes exceeding the width. The dimensions of two complete 

 examples are: length of pedicle valve 13.5 mm. and 16.8 mm., length of 

 brachial valve 11.5 mm., and 14.6 mm., greatest width 8.2 mm. and 12 mm., 

 thickness 9.8 mm. and 12.2 mm. 



Pedicle valve gibbous, the curvature abruptly changed in mature ex- 

 amples near the mid-length of the valve, where it is bent in a subgenicu- 

 late manner, the curvature to the postero-lateral margins is abrupt, the 

 surface becoming inflected to the cardinal extremities, towards the 

 antero-lateral and anterior margins the curvature is rather gently convex 

 to the line of geniculation, beyond which the surface drops abruptly to the 

 margins; mesial sinus originating at the line of geniculation, usually flat 

 in the bottom, slightly or strongly depressed towards the margin, the 

 median, flattened portion a little produced anteriorly in a short, rounded, 

 lingual extension ; beak prominent, strongly incurved, its apex nearly or 

 quite in contact with the umbo of the opposite valve, pierced by a large, 

 subovate foramen which encroaches wholly upon the umbonal region of 

 the valve, the delthyrium hidden by the incurvature of the beak, in con- 

 tact with the foramen only at its apex, entirely filled by the pseudodel- 

 tidium. Internally the dental lamellae are well developed and reach an- 

 teriorly from the beak nearly one-fourth the total length of the valve. 



Brachial valve a little less convex than the pedicle, the surface genicu- 

 late as in the opposite valve, curving rather abruptly to the postero- 

 lateral margins and more gently to the antero-lateral and anterior mar- 

 gins up to the line of geniculation beyond which it drops abruptly to the 

 margin; in front of the line of geniculation the median portion of the 

 valve is marked by three longitudinal folds separated by subangular or 

 rounded furrows, the median one of the three folds is opposite the slight 

 lingual extension from the anterior margin of the sinus of the pedicle 

 valve, it may be somewhat elevated above the two lateral folds, even with 

 them or depressed between them; the beak pointed, incurved beneath 

 that of the opposite valve. Internally the socket plates are distinct from 

 the crural plates, the latter are attached to the inner surface of the valve 

 for more than one-fourth its length anteriorly from the beak, a little less 



